Basic Knowledge for Electric Vehicle Insulation

Since the electric vehicle insulation failure will cause the electric vehicle to be unable to run, it is particularly important to add DC insulation monitoring and ground fault protection devices to the electric vehicle. This article will introduce you to the relevant content of electric vehicle insulation from the definition of electric vehicle insulation, the methods and principles of electric vehicle insulation detection, the role of insulation monitoring devices for electric vehicle insulation protection, and the recommendation of electric vehicle insulation monitoring devices.

What is electric vehicle insulation?

Electric vehicle insulation generally refers to the insulation between the electric vehicle and the ground (or other grounded structures) to prevent current flow in unwanted parts and ensure safe operation. Tram systems typically use electric current to drive the vehicles, and this current needs to be transferred through contact between the track and the vehicle. To prevent current from escaping where it is not needed, measures need to be taken to insulate the tram system.

Methods and principles of electric vehicle insulation Detecting

There are currently two mainstream insulation detection methods, the bridge method, and the AC injection method, but this function is implemented by the battery management system BMS. The bridge method is also called the passive detection method. The main reason is that high voltage is required for insulation detection. The AC injection method is also called the active detection method because the insulation detection function can be completed when 12V lead acid is powered on.

Item	Bridge method	Ac injection method
Sampling accuracy	High	Ordinary
Sampling time	When the insulation is normal, the sampling time is long. The lower the insulation value, the shorter the sampling time.	The first sampling time after power-on is long
Circuit configuration	High voltage is required	No high voltage required, AC pulses required
Detection position	High voltage positive/body ground high voltage negative/body ground	High voltage bus/body ground
EMC performance	Better	Generally
Cost	Can be multiplexed with high-voltage detection and circuits such as precharge detection and relay diagnosis.	High voltage detection circuit cannot be reused
Stability	Better	Better

Electric vehicle insulation principle of bridge method

The working principle of the bridge method is that the BMS calculates the insulation resistance of the positive electrode/body and the negative electrode/body by detecting the partial voltage change between high voltage positive and high voltage negative. The detection principle is as follows:

1. Close switch S1 and close switch S2: BMS detects the voltages of V1 and V2;
2. Close switch S1 and open switch S2: BMS detects the voltage of V1’;
3. Open switch S1 and close switch S2: BMS detects the voltage of V2’;
4. According to the above three steps, knowing the total voltage U of the battery and the voltage dividing resistance of the positive and negative bridge arms and their ratio, three equations can be listed U=aV1+bV2,
5. Solve the equation according to this equation to obtain: positive electrode/casing resistance = Rp, negative electrode/casing = Rn
The two resistance values are the insulation values we usually read on the electric vehicle. The above is the detection principle of the bridge method.

Function of insulation monitoring device on electric vehicle insulation

Regarding personal electric shock, here are several hypothetical situations. Figure left shows that the DC negative pole is poorly insulated and touches the positive pole, which can lead to electric shock; Figure right shows that the human body touches the car body or pile body, which can easily cause electric shock. A current that threatens life in a short period of time is called a fatal current. For example, a current of 100 mA passing through the human body for 1 second can be fatal. However, the general DC system cannot quickly and accurately detect leakage caused by personal electric shock. Since the prerequisite for an electric shock accident is the reduction of the insulation of the DC positive or negative pole to the ground, for this reason, a DC ground EV charger insulation monitoring device is important for EV chargers or electric vehicles to protect you from electric shock.

GYID Insulation monitoring device for electric Vehicle

AC/DC IT System, Up to 1000V, Can bus communication, widedly used for EV chargaer & electric vehicle

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Blue Jay Technology GYID insulation monitoring device for electric vehicle is din-rail mounting, easy to use, and small in size. The voltage range can be protected in 0~1000 Vd.c. DC floating (IT) system and 0~750 Va.c. AC floating (IT) system. Resistance measurement range: 0~50 MΩ, when it exceeds 50 MΩ Default output is 50 MΩ. In a DC system, the insulation resistance of the positive and negative poles of the DC system to the ground can be independently measured.

In specific electric vehicle applications, insulation resistance can also be reliably monitored under strong interference or complex driving conditions, such as acceleration/deceleration, braking, and energy recovery. In AC systems, it can suppress the interference of high-frequency harmonics of voltage and accurately measure the insulation resistance to the ground of the entire AC system.

Our advanced GYID series Can Bus insulation monitors can be used for ground insulation in electric vehicle power battery high-voltage systems, hybrid vehicle high-voltage systems, hydrogen vehicle high-voltage systems, energy storage systems, other DC floating systems, AC floating systems, etc. monitors. It can also be used in charging piles and charging stations.